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Help. Lousy Electrical Gremlin and Codes


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So here's the story; bought a truck I should not of. Host of issues i've been working my way through to fix. Cab Corners, Door Sills, E-brake/Parking Brake Complete incl backing plates, idler arm, pitman arm, lwr ball joint, exhaust manifold gaskets and studs/bolts, air bag sensors and wire broke on passenger presence sensor (need to remove seat) Wheel Bearing, fuel filter, rear brake lines and heated seats (that was a straight fwd fix as plug had come undone under drivers seat)


So fixed everything and got the trucked safetied, registered and plated.


Picked the truck up

started and drove fine, got to gas station to top it off.

restarted truck and rough idle with "Reduced Pwr" advisory.

shut the truck off then back on and restarted.

Advisory gone but chk engine light was on, everything else seems normal. Drove home.

Was approx 15km into the drive home and turned on the high beam lights.......darkness. all headlights went out.

Back to low beam and I could see again. Tried High beam and lights out.

Back to low. At one point it seemed like a low beam light went out so flicked high beam lever off then on, all low beams appeared to be back on.

Pulled into the Drive way and parked (kind of odd that we drive on Parkways and Park in Driveways?)

Flicked high beams on and off and Voila! Truck starts stumbling and "Reduced Power" advisory is back.

Shut Truck off, then back on. High Beams now work (WTF!) and Advisory gone, idles normal but RPM Gauge reads below "0" RPM. Needle moves as you press and release the Throttle but is below 0 at idle.

So shut it down, walked inside and had a drink (more than one but we don't need to get into that)


Went out this morning for the standard lift the hood, look underneath and scratch ones head.

Started Truck. Check Eng light still on and RPM Gauge reading normal.

Pulled the following codes

P1516 Throttle Actuator Control Module Throttle Actuator Posn

P1518 Electronic Throttle Module To PCM Communication

P2108 THrottle Actuator (TAC) Module Performance

P0157 HO2S Circuit Low Voltage Bank 2 Sensor


As well noticed now that when I started it, all gauges appeared good except the Oil Pressure Gauge was full pegged to the right (almost at the 4 oclock position), with the truck off all gauges at 0 but Oil Press Gauge is above 550KPA (approx 2 oclock position)


I understand electrical systems and this nightmare has me leaning towards a bad/loose gnd or partially broken wire somewhere but I have no idea where to start. Understand the thigh bone is connected to the knee bone but how one goes from High Beam switch to "Reduced Pwr" advisory and funky gauges I have no clue.



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While reading your post my first thought was bad ground too. I would start by checking battery cable ends and clean them and then chase down all engine to firewall grnd's and chassis grnd's.


Take them apart and scrape the terminals and take a bit of sandpaper to the point's they mount to.


I would also look at the connections to the headlight relay and take a look at the major wiring harness connectors.


(Checking for corrosion).


Best luck Brother. Let us know how it goes.


Points for saving a truck that obviously needed some TLC. :cheers:

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I take it you found the problem? I can't do from my phone. I usually do from a computer. The file size is limited on the site. When I upload I send from my iPhone and send at a reduced file size.

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Haven't found yet but have a question about a particular wire coming off a loom located back right hand side of the engine. Loom is on top with a wire that comes out and runs down behind the engine block. Wondering if it is a gnd wire?


Still don't know how to upload a photo of the loom in question. As well found a major gnd attached to back left hand firewall that is frayed (not completely through) and corroded.

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Ground typically big strap type wires. I know there is one from engine rear head to frame. There are others but we would need to see pic. Like I said I can't do from a phone the Mobil version doesn't have the capability the full site version has ability to upload a pic.

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What color is the wire at the right rear of the engine? That might indicate if it is a grnd.


Is the frayed grnd webbing and is the webbing corroded or is the corrosion at the attachment points? Either way I would clean it up and replace the wire or strap whichever it is.


I resize my pics to 640 X 480 pixels and upload them to a photo hosting site, (I use photobucket), and then direct link them to the response box using the "insert image" prompt in the header above the response box.


I only use my desktop to attach photos to posts. Don't know nothing about posting from a phone. I've got a dumb phone and it's still smarter than I am. :jester:

Edited by Downeast Johnny (see edit history)
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Wire is covered with tape and black protective sleeve on the back right.

The corroded one is webbing type. Corroded & frayed at attachment point and green surface corrosion on remainder.


Ack the requirement to use a photo hosting site.

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  • 2 months later...

So I think we have come to the conclusion of this particular story. Here is how it has ended.


Gnds at the back of the block;

Passenger Side back of block (accessible from the top) is G103

Drivers Side back of block (accessible kind of from under neath (this Gnd is the one the vehicle bonding strap runs to)) G104

Front left bottom of Rad Support G101 (this one has a couple of gnds running to it incl Headlights)


Usually if you are having intermittent "Reduced Pwr Advisory" with either ABS or Traction Control issue it most likely will be G103 or G104.

Mind was really odd as the snag was tied to switching from Lo to Hi Beam and that circuit is not common to Throttle Body, Throttle Position Sensor or Throttle Control Module.


After trying to de-snag I finally gave up and brought it to my local shop (I did check all the connectors to the Throttle body and wires). When I explained the snag he was scratching his head saying "it should not do that." He took it in a gave it a go. First he checked and replaced the Gnds (G103 and G104) recleaned G101 checking all the connectors and lugs (replaced the bonding strap). No Joy, snag still remained. He then pulled the headlight pods to take a look at their wiring.


Found out the previous owner had installed HID bulbs and their controllers/ballasts. That install was completely buggering things up. HID's pulled and disconnected. New OEM bulbs reconnect and installed and.........Voila! Everything works. Yaaaahhhhhh!


Side note as I was trying to de-snag my Oil Pressure Gauge went wonky. Would not return to Zero PSI/KPA on shut down and when running ran really high. Stepper Motor had gone in the Gauge Cluster. Ordered new ones on line (approx $24.00) pulled the gauge cluster, took apart, removed and re-solderd new one and now works fine. Several good video's on Youtube on how to do this. Need couple small sockets, ratchet, solder sucker and soldering iron. To remove took maybe 15 mins same on install. Un Plugging Wire Harness from back of Cluster can be a pain. Squeeze tabs together well and wiggle and pull. When inserting make sure you insert it straight in as you don't wish to bend a pin.


Only one thing left is the Cabin Temp Sensor Fan behind the small grill above Drivers head. It's buzzing a little.


That's it for now and thanks for the help along the way.



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